This invention relates to radial lip seals. More particularly, it relates to radial lip seals which can accommodate significant shaft-to-bore misalignment or dynamic shaft runout.
Lip seals are usually molded of a resilient elastomeric or polymeric material. They are secured in fluid tight relation to a housing and surround a rotating shaft which extends through an aperture in the housing wall. The sealing lip is in sealing relationship to the shaft to contain the fluid in the housing.
Lip seals components or elements include a rigid case or retainer to add rigidity and unitize the seal assembly. The case also aids installation, withdrawal and retention of the seal relative to the housing. The resilient body includes a secondary seal to seal against the housing and one or more resilient sealing lips which are maintained in sealing contact with the shaft.
Lip seals experience a wide variety of uses. Commonly such seals are employed in automotive applications operating temperatures and pressure, shaft speed, and the make-up of the medium to be contained, dictate the specifics of a particular construction. Typically, however, the rigid component or retainer is formed of hard plastic such as phenolic, steel or stainless steel and the resilient lips are defined by elastomeric or polymeric members such as molded rubber, polytetrafluroethylene or other known materials. The resilient element may be molded as a single body or may comprise a plurality of separate elements connected together in fluid tight relation.
The nature of lip seal applications expose the seal to conditions of significant shaft movement relative to the surrounding housing. Shaft misalignment and run-out challenge the effectiveness of the seal.
Examples of extreme service include automotive air conditioning compressors where the shaft is typically driven by a belt and pulley through an electric clutch. Compressor design results in shaft wobble, bending distortion and misalignment of the shaft axis relative to the housing aperture.
Efforts to provide a lip seal to accommodate shaft run-out or misalignment include use of extended conical shapes, multiple lips and other variations of the resilient element. A particularly effective arrangement is disclosed in copending U.S. Pat. No. 5,503,408 issued on Apr. 2, 1996, and assigned to John Crane Inc., Morton Grove, Ill. This seal embodies multiple resilient lips which may be integrally molded into the resilient component. The sealing lip effectiveness is augmented by an auxiliary or alignment lip which is interposed between the shaft and the sealing lip. Under conditions of misalignment, the auxiliary lip contacts the underside of the primary sealing lip and causes a displacement of that lip in the direction of displacement of the shaft relative to the center or axis of its associated housing bore. Such displacement causes the primary sealing lip to "follow" the shaft and, thereby, maintain the integrity of its sealing relation to the shaft.
Another effort to address the misalignment problem is reflected by U.S. Pat. No. 5,370,404, entitled "Radial Lip Seal With Interposed Bearing". That patent discloses incorporation of a roller bearing into the seal assembly to counteract misalignment or shaft displacement from a concentric relation to the associated bore. The approach shown presents other inherent difficulties deleterious to seal performance and longevity.
The disclosed bearing is interposed between the lip seal and the medium sealed within the housing. This relationship restricts access of the contained fluid medium to the sealing lips which seal against the shaft. The cooling effect provided by the sealed medium will be severely diminished and the seal will, therefore, experience excessive heat during operation which could result in heat aging of the lip element.
Also, the roller bearing arrangement disclosed in U.S. Pat. No. 5,370,404 involves very close tolerances between the bearing races, balls and associated shaft and housing connection. Such a bearing requires lubrication to ensure durability and therefore must be positioned internally of the housing for access to such lubrication.
U.S. Pat. No. 4,968,044 shows a lip seal excluder arrangement for an axle which incorporates a thrust bearing made of a hard plastic such as an internally lubricated nylon composition. The thrust bearing is loosely connected to a rigid retainer element of a lip seal assembly. It is free to rotate relative to the retainer. It is also disposed in the lubrication medium. Moreover, concentricity between a shaft and the associated housing is not addressed by the structure disclosed.
The seal of the present invention accommodates shaft runout or eccentric operation utilizing features not disclosed in the aforementioned U.S. Pat. Nos. 5,370,404 and 4,968,044.
Appliances such as dishwashers present a somewhat different problem which dictates against use of lip seal. Assembly tolerances permit shaft, to housing bore misalignment which exceeds the maximum allowable shaft run-out for a typical radial lip seal. Traditionally therefore other forms of seals were required.
The seal of the present invention addresses the problem and renders lip seals suitable for appliance applications.